Mail Archives: djgpp/1997/01/09/12:21:01
Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk> wrote:
>The problem is, I think, with the vsync() call. Win95 seems very erratic
>in it's handling of retrace syncing. Sometimes it works, sometimes it
>doesn't, which is very irritating (if only IBM had seen fit to include a
>retrace interrupt in the VGA design!).
This may not have been in the *original* IBM VGA card, but according
to my old book in programming for PC video subsystems, the EGA, the
VGA, and the MCGA supports generating a Vertical Interrupt on IRQ2
whenever vertical retrace starts, and explains how this is done. On
the EGA/VGA, these interrupts appears to be controlled by the CRTC
Vertical Retrace End register (CRTC register 11h) bits 4 and 5, though
I haven't really studied this in detail.
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